The use of reinforced cement panels is well known in industries such as the ceramic tile industry. Generally, cement panels or boards contain a core formed of a cementitious material which may be interposed between two layers of facing material. The facing materials employed typically share the features of high strength, high modulus of elasticity, and light weight to contribute flexural and impact strength to the high compressive strength, but brittle material forming the cementitious core. Typically, the facing material employed with cement panels is fiberglass fibers or fiberglass mesh embedded in the cementitious slurry core. Fiberglass performs particularly well in this application. Fiberglass provides greater physical and mechanical properties to the cement board. Fiberglass is also an efficient material to reinforce the cement panels because of its relatively low cost compared with other high modulus materials.
Cementitious backerboard comprises a panel having a core layer of light-weight concrete with each of the two faces covered with a layer of reinforcing fabric bonded to the core layer. Such cementitious backerboards are described in U.S. Pat. No. 3,284,980 P. E. Dinkel, incorporated herein by reference in its entirety. These panels are nailable and can be readily fastened to the framing members. Furthermore they are substantially unaffected by water and consequently find extensive use in wet areas such as shower enclosures, bathtub surrounds, kitchen areas and entryways, as well as on building exteriors.
Cementitious backerboards are generally produced using a core mix of water, light-weight aggregate (e.g., expanded clay, expanded slag, expanded shale, perlite, expanded glass beads, polystyrene beads, and the like) and a cementitious material (e.g., Portland cement, magnesia cement, alumina cement, gypsum and blends of such materials). A foaming agent as well as other additives can be added to the mix.
The reinforcing fabric most generally employed is a fiber glass scrim and, in particular, is a woven mesh of vinyl coated fiber glass yarns. The yarn count per 2.54 centimeter (1 inch) of the fabric varies from 8×8 to 12×20, depending upon the size of the openings in the mesh or scrim for passage of the bonding material through the fabric. Other pervious fabrics having suitable tensile strength, alkali resistance and sufficiently large pores or openings may be employed.
Commonly the reinforcing fabric is bonded to the surface of the core layer with a thin coating of Portland cement slurry, with or without some fine aggregate added. Alternatively, the core mix can be sufficiently fluid to be vibrated or forced through the openings of the reinforcing fabric to cover the fabric and to bond it to the core layer. This is described in U.S. Pat. No. 4,450,022 of Galer, the disclosure of which is incorporated herein by reference in its entirety.
US Patent application publication number 2009/0011207, incorporated herein by reference, discloses a fast setting lightweight cementitious composition for construction of cement board or panels. The cementitious composition includes 35-60 wt. % cementitious reactive powder (also termed Portland cement-based binder), 2-10 wt. % expanded and chemically coated perlite filler, 20-40 wt. % water, entrained air, for example 10-50 vol. %, on a wet basis, entrained air, and optional additives such as water reducing agents, chemical set-accelerators, and chemical set-retarders. The lightweight cementitious compositions may also optionally contain 0-25 wt. % secondary fillers, for example 10-25 wt. % secondary fillers. Typical filler include one or more of expanded clay, shale aggregate, and pumice. The cementitious reactive powder used is typically composed of either pure Portland cement or a mixture of Portland cement and a suitable pozzolanic material such as fly ash or blast furnace slag. The cementitious reactive powder may also optionally contain one or more of gypsum (land plaster) and high alumina cement (HAC) added in small dosages to influence setting and hydration characteristics of the binder.
Other methods of manufacture of cement boards are disclosed in U.S. Pat. No. 4,203,788 to Clear, which discloses a method and apparatus for producing fabric reinforced tile backerboard panel. U.S. Pat. No. 4,488,909 to Galer et al. describes in further detail, in column 4, the cementitious composition used in a cementitious backerboard. U.S. Pat. No. 4,504,335 to Galer discloses a modified method for producing fabric reinforced cementitious backerboard. U.S. Pat. No. 4,916,004 to Ensminger et al. describes a reinforced cementitious panel in which the reinforcement wraps the edges and is embedded in the core mix. The disclosures of all of the above listed US patents are incorporated herein by reference in their entirety.
Fiberglass, however, has a major disadvantage. It lacks resistance to chemical attack from the ingredients of the cements. Common cements, such as Portland cement, provide an alkaline environment when in contact with water, and the fiberglass yarn used in reinforcement fabrics is degraded in these highly alkaline conditions. To overcome this problem, protective polymeric coatings, such as polyvinyl chloride solution coatings, are applied to the fiberglass. Although these coatings reduce fiberglass degradation, the integrity of the protective coating on the fiberglass yarns is critical to the success of the concrete panel. Furthermore, the coating rapidly degrades with heat, which typically occurs during the curing of the cementitious boards. Therefore, excess fiberglass must be included to ensure a minimum amount of strength over the life of the cement boards.
Efforts have been made to reinforce wall board through use of fabric reinforcement secured in position to the surface of the board with an adhesive as in U.S. Pat. No. 1,747,339 A to Walper, incorporated herein by reference. In Walper the fabric reinforced wall board is also coated with water-proof or moisture resistant material to protect the edges of the board against moisture.
U.S. Pat. No. 6,187,409 B1 to Mathieu, incorporated herein by reference discloses cementitious panel is reinforced with a fabric at its surface and the longitudinal edges are reinforced with a network of fibers. A continuous band of synthetic alkali-resistant, non-woven fabric completely covers the edge areas of the board with a U-shaped reinforcing mesh to make the edges resistant to impact.
US published application US2004/0219845 to Graham, incorporated herein by reference, proposed to use a carbon fiber fabric to form a scrim that wraps the board and its edges and is bonded to the board surface with an adhesive. Polyvinyl alcohol, acrylic, polyvinyl acetate, polyvinyl chloride, polyvinylidene chloride, polyacrylate, acrylic latex or styrene butadiene rubber, plastisol are disclosed as adhesives.
U.S. Pat. No. 6,054,205 to Newman et al. and related U.S. Pat. No. 6,391,131 to Newman et al, incorporated herein by reference, disclose glass fiber facing sheets comprising an open mesh glass scrim having a plurality of intersecting continuous multifilament yarns. The multifilament yarns are bonded at their crossover points to form a dimensionally stable scrim which can be used to make a cement board with facing sheets mechanically integrated into opposed surface portions of a cementitious core. A conventional method for making the glass fiber facing sheet and a method of making a cement board with this glass facing sheet is disclosed in the related U.S. Pat. No. 6,391,131.
U.S. Pat. No. 7,045,474 to Cooper et al. proposed using composite fabric for reinforcement, particularly tensile reinforcement of cementitious boards. In particular it discloses mesh constructed from fabric of high modulus strands made from bundles of glass fibers encapsulated by alkali and water resistant thermoplastic material for embedment within the cement matrix to improve tensile strength and impact resistance of the cement board. The reinforcement fabric is disclosed as a woven knit, nonwoven or laid scrim open mesh fabric having mesh openings of a size suitable to permit interfacing between the skin and core cementitious matrix material. In a preferred construction, the fabric is in a grid-like configuration having a strand count of between about 2 to about 18 strands per inch in the length and width directions. The mesh is preferably composite yarns or rovings of an elastic core strands such as E-glass fibers or similar glass fibers sheathed in a continuous coating of water and alkali resistant material including, sheathed in material.
U.S. Pat. No. 7,354,876 and U.S. Pat. No. 7,615,504 to Porter et al propose a reinforced cementitious board and methods for making the reinforced board. The reinforced board comprises a cementitious core and a reinforcing fabric embedded into at least a portion of the core on at least one surface of the core. The reinforcing fabric is not in the form of a fiberglass mesh. The reinforcing fabric includes a specific construction including a plurality of warp yarns having a first twist (turns/inch), a plurality of weft yarns having a second twist greater than the first twist, and a resinous coating applied to the fabric in a coating weight distribution of less than about 2.0:1 based upon the weight of the coating on the weft yarns over the weight of the resin on the warp yarns.
One commercially woven fiberglass mesh is available from Bayex under the number 0040/286. BAYEX 0040/286 is a Leno weave mesh having a warp and weft of 6 per inch (ASTM D-3775), a weight of 4.5 ounces per square yard (ASTM D-3776), a thickness of 0.016 inches (ASTM D-1777) and a minimum tensile of 150 and 200 pounds per inch in the warp and weft, respectively (ASTM D-5035). It is alkali resistant and has a firm hand. Other fiberglass meshes having approximately the same dimensions have opening of sufficient size to allow a portion of the gypsum/fiber mix to pass through the mesh during formation of the board may be used.
Another commercially available woven fiberglass mesh is available from Bayex under the number 0038/503. BAYEX 0038/503 is a Leno weave mesh having a warp of 6 per inch and weft of 5 per inch (ASTM D-3775), a weight of 4.2 ounces per square yard (ASTM D-3776), a thickness of 0.016 inches (ASTM D-1777) and a minimum tensile of 150 and 165 pounds per inch in the warp and weft, respectively (ASTM D-5035). It is alkali resistant and has a firm hand.
Another woven fiberglass mesh available from BAYEX under the number 0038/504. BAYEX 0038/504 is a Leno weave mesh having a warp of 6 per inch and weft of 5 per inch (ASTM D-3775), a weight of 4.2 ounces per square yard (ASTM D-3776), a thickness of 0.016 inches (ASTM D-1777) and a minimum tensile of 150 and 165 pounds per inch in the warp and weft, respectively (ASTM D-5035). It is alkali resistant and has a firm hand. Other fiberglass meshes having approximately the same dimensions have opening of sufficient size to allow a portion of the gypsum/fiber slurry to pass through the mesh during formation of the board may be used.
Yet another woven fiberglass mesh is available from BAYEX under the number 4447/252. BAYEX 4447/252 is a Leno weave mesh having a warp of 2.6 per inch and weft of 2.6 per inch (ASTM D-3775), a weight of 4.6 ounces per square yard (ASTM D-3776), a thickness of 0.026 inches (ASTM D-1777) and a minimum tensile of 150 and 174 pounds per inch in the warp and weft, respectively (ASTM D-5035). It is alkali resistant and has a firm hand. Other fiberglass meshes having approximately the same dimensions have opening of sufficient size to allow a portion of the gypsum/fiber mix to pass through the mesh during formation of the board may be used.
There remains a need for an improved cementitious panel, e.g. a cement board reinforced with reinforcing fabric scrim or non-woven fabric layers which provides for more penetration of the cement slurry through the fabric scrim during manufacture of the cement board. There also remains a need for a cement board with improved runnability and field performance (e.g. score and snap).